During oil production, it may become necessary to perform maintenance work in a well or to open a production well. Such well work is known as well intervention. A production casing is arranged inside the well and is closed by a well head in its upper end. The well head may be placed on shore, on an oil rig or on the seabed.
In order to lower and raise the tool into and out of the well and supply the tool with electricity, the tool is connected to a wireline at its top, which is fed through the well head. In order to seal the well while performing the operation using the tool, the wireline passes through a high-pressure grease injection section and sealing elements for sealing around the wireline.
In order to seal around the wireline as it passes through the grease injection section, high-pressure grease is pumped into the surrounding annulus to effect a pressure-tight dynamic seal which is maintained during the operation by injecting more grease as required. A slight leakage of grease is normal, and the addition of fresh grease allows for the consistency of the seal to be maintained at an effective level. In this way, grease leaks from the grease injection section into the sea during an intervention operation, which is not environmentally desirable. Due to the increasing awareness of the environment, there is a need for a more environmentally friendly solution.